They are the Yeoman of the Guard - the bodyguards of the British monarch - and they're about to conduct a search of the cellars of the Houses of Parliament before the official State Opening by the Queen.

What are they searching for? Well, these days it's just a traditional part of the ceremony, but when it began in the 17th century, it had a very serious purpose.

They were checking for gunpowder - and all because of a group of men including Guy Fawkes. You may have heard of him.

Guy Fawkes was part of a group of men who wanted to blow up the Houses of Parliament in London but he was caught red-handed with the explosives. All this happened in 1605, more than 400 years ago, and nowadays we call the story the Gunpowder Plot.